1. Field of the Invention
The present invention relates generally to a control system for controlling wheel slippage, such as an anti-skid control system for a brake system of an automotive vehicle and a traction control system for controlling driving torque to be distributed to vehicular wheels. More particularly, the invention relates to a projection of a vehicle speed representing data for facilitating wheel slippage dependent brake control, which projected vehicular speed representing data precisely correspond to an actual vehicle speed.
2. Description of the Background Art
One typical construction of an anti-skid brake control system is disclosed in Japanese Patent Second (examined) Publication (Tokko) Showa 51-6305. The disclosed anti-skid brake control system employs an acceleration sensor for monitoring an acceleration exerted on the vehicular body for producing an acceleration indicative signal, and a wheel speed sensor for monitoring rotation speed of the vehicular wheel for producing a wheel speed indicative signal. The system differentiate the wheel speed indicative signal to obtain an acceleration data for triggering anti-skid control while the wheel deceleration (negative value of acceleration) increases across a predetermined deceleration criterion, e.g. -1.O G. Upon triggering anti-skid brake control, an instantaneous wheel speed indicative signal value is latched as a data representative of an initial value of a vehicular speed. The acceleration indicative signal produced by the acceleration sensor is fed to an integrator which becomes active when a vehicle speed becomes higher than a predetermined speed, e.g. 5 km/h. The integrator circuit integrates the acceleration indicative data by time to derive a vehicle speed variation indicative data. The vehicle speed variation data is added to the initial vehicular speed representative data latched upon initiation of the anti-skid brake control to derive a vehicle speed data projected based on the vehicular body acceleration. The projected data will be hereafter referred to as "projected vehicle speed data". The projected vehicle speed data is compared with the instantaneous wheel speed indicative signal value to derive a wheel slippage.
As is well known, anti-skid brake control is performed through a known process to hold braking pressure constant (HOLD mode) when wheel deceleration increases below the deceleration criterion; to decrease braking pressure (RELEASE mode) when the wheel slippage increases across a predetermined wheel slippage criterion, e.g. 15%; to hold the braking pressure (HOLD mode) when the wheel acceleration increases across a predetermined wheel acceleration criterion, e.g. +0.6 G; and to increase braking pressure (APPLICATION) mode when wheel slippage is decreased across the wheel slippage criterion.
In the process set forth above, it is essential to precisely obtain the projected vehicular speed for obtaining high precision in derivation of precise value of wheel slippage. However, prior processes tend to accumulate error in detection of vehicular body acceleration, to cause substantial error in derivation of the vehicular speed variation indicative data and, thus, tend to cause substantial error in the derivation of the wheel slippage. Therefore, such prior proposed systems have not been satisfactorily precise in performing anti-skid brake control at a sufficient precision level.